Digestive System Flashcards
What is digestion?
Physical and chemical disruption of food for absorption of nutrients
What are the 4 accessory organs to the digestive system?
Salivary glands, gall bladder, pancreas, liver
Name 6 things about saliva
1) Contains amylase and lipase
2) Bacteriostatic (IgA)
3) High calcium (protects teeth)
4) Alkaline
5) Assists swallowing
6) Protects the mouth
What are the four layers of gut wall? Which is the layer where arteries/veins/glands and nerves are found? What are the other layers made up of?
Mucosa
Sub mucosa
Muscular externae
Serosa
Mucosa - stratified squamous non-keratinised epithelium and lamina propria (CT)
Sub Mucosa is connective tissue where arteries/veins/glands and nerves are found
Muscular externae has 2 layers of smooth muscle - outer longitudinal, inner circular
Serosa made up of simple squamous epithelium and connective tissue
8 functions of the GI tract? (think from mouth down)
1) Entry of food
2) Disrupt food
3) Store food
4) Digest food
5) Kill pathogens
6) move food along
7) Absorb nutrients
8) Eliminate waste
What 5 groups of nutrients do we need to absorb?
Vitamins Minerals Fatty acids Amino Acids Sugars
What does saliva contain to make it bacteriostatic?
Immunoglobulin A antibody
What 2 enzymes does saliva contain
Lipase Amylase
How does a bolus get swallowed?
Initial voluntary muscle contraction of oesophagus, then involuntary, rapid peristaltic movement
Where is the fastest GI transport?
Entry exit - rest is comparatively low
What is oesophageal epithelium and why is it well suited?
Stratified squamous epithelium non keratinised - can withstand abrasion
Where do you find lamina propria in the body?
Mucosal areas - e.g. GI, Lung, GU
What is the lamina propria? What does it contain?
Thin layer of loose connective tissue or dense irregular connective tissue laying under the epithelium. This plus epithelium (+/- muscle) = mucosal membrane. Contains Peyer’s patches
How does mechanical and chemical disruption of food begin in the mouth?
Mastication
Amylase/lipase
What is a role of the muscularis externae layer of gut wall?
Peristalsis
How does the stomach aid physical and chemical digestion?
Physical - Churning - 3 muscle layers and rugae
Chemical - Add HCl and Pepsin
Why do we need the stomach to be a temporary food store?
Can eat faster than we can digest
How does the stomach not digest itself
Mucus
What is chyme? Is it Hypo or hypertonic?
acid, enzymes, partially digested food that has been agitated by stomach. It is hypertonic
What are the roles of HCl and Pepsin in the stomach?
Protein breakdown - pepsin
Disinfect food - HCl
What 5 cells are in a gastric gland in the stomach? What do they do?
Goblet like cells - secret mucus
Stem cells - regenerate
Parietal cells - secrete H+ into lumen and HCO3- into capillaries which move it to surface mucous cells
Chief cells - secrete pepsinogens –> pepsins
Enteroendocrine cells - secrete gastrin (hormone that stimulates acid secretion)
What are the roles of the duodenum (6)
Draw in water and neutralise chyme (isotonic) with bicarbonate rich mucus, absorb iron. Receives bile from gallbladder. Pancreas and liver secrete alkali to neutralise acidic chyme. Pancreas, liver and intestine secrete specific enzymes which act with bile to complete digestion of chyme.
What glands secrete bicarb rich mucus from duodenum?
Brunner’s glands
What do the pancreas and liver secrete into the duodenum (2)?
alkali, enzymes
What do the enzymes from pancreas and intestine do (4)?
Cleave peptides to amino acids
Cleave polysaccharides to monosaccharides
Break down and reform lipids
Break down nucleic acids
Is absorption passive or active
active
How does the jejunum maximise surface area (2)?
- place circulares
- villi
What is the epithelium of the jejunum? What other cell is there?
Simple columnar with goblet cells and villi
What is a lacteal?
Dilated lymphatic vessel
Whats the function of the jejunum?
Absorbs most sugars, aa’s, fatty acids
What does the ileum do?
Absorbs vit12, bile acids and remaining nutrients
By end of ileum what still needs to happen?
Water needs to be reabsorbed - colon
Whats the order of the colon starting with caecum?
Caecum, ascending, transverse, descending, sigmoid
What is the function of colon?
Absorb water and electrolytes
What are Crypts of Lieberkuhn
Simple columnar epithelium in crypts - glands - cells produce a lot of mucus, absorb water and electrolytes among other things
How long is the transit in colon?
20 hours
Where do contents await expulsion?
in colon NOT rectum
Where is most bacteria held in GI? is it anaerobic or aerobic? Where is it lost?
Colon, 99% anaerobic and lost in faeces
What are the functions on bacteria in colon? (3)
1) Synthesis of vitamins K, B12 etc (absorbed by colon)
2) Breakdown of primary to secondary bile acids (absorbed by colon)
3) Conversion of bilirubin to non pigmented metabolites that are reabsorbed in the colon
How is the GI controlled? (3)
Endocrine
Nervous
Paracrine (esp stomach)
How is the GI tract controlled by nervous system?
Somatic- mouth, swallowing, anus
Autonomic - peristalsis
How many nerve plexuses are there along the GI tract?
2
Which two paracrine substances control GI? What do they do?
Histamine - controls acid production in stomach
Vasoactive substances - affect blood flow in gut
What are the three major endocrine substances that control the GI?
1) Gastrin -
2) CCK (Chlycystokinin)
3) Secretin
What is gastrin and what does it do (1) ? Where is it released from?
Hormone stimulates secretion of HCl from parietal cells in the stomach. Released from G cells of pyloric antrum of stomach, pancreas and duodenum
What is CCK and what does it do (3) ? Where is it secreted?
Hormone - secreted by enteroendocrine cells of the duodenum. Hunger suppressant. Promotes release of enzymes from pancreas, bile from gallbladder
What is secretin? What does it do (3)
Hormone - promotes bicarb secretion from duct cells of pancreas, promotes bile production by liver, inhibits secretion of acid by parietal cells of stomach.
Where is bit B12 absorbed from?
Ileum
Where is Iron absorbed from?
Duodenum
Where are electrolytes absorbed from?
Colon
Where are AA, fatty acids and carbs absorbed from?
Jejunum
Where are bile acids and remaining nutrients absorbed from?
Ileum
What are Peyers patches?
Aggregations of lymphocytes present in the Lamina Propia
What are two sources of innervation to the gut located in the gut wall?
Myenteric Plexus
Submucosal Plexus
What three things is bile made up of?
Bile salts
Water
Alkali
How long is the duodenum and what shape?
20-25cm shortest part and C shaped